Numerical Investigations on a deployable lightweight radar antenna for a satellite based earth monitoring system

Kurzfassung

Key point of this thesis is the numerical investigation of the static and dynamic behaviour of an unfolded lightweight radarantenna, a so called gossamer structure. These structures are special deployable and lightweight for the use in space. They are constructed to unfold from a packed state for storage and transport into orbit to a deployed state for the use in orbit. This special an-tenna will be used for synthetic aperture radar (SAR) to monitor the earth and its activities, e.g. glacier movements, tectonic activities or changes in its vegetation. For this use, the antenna shall comply with very strict atness requirements after uncoiling from convoluted state. This project is currently carried out by the European Space Agency (ESA) and the German Aerospace Center (DLR) at its laboratories in Brunswick, Germany. The unfolding process is very precarious for the structure. Therefore, the design has to avoid any possible damage to the structure resulting from the deployment. Dynamic problems were investigated to obtain the best possible structural damp-ing in a micro- to zero gravitation condition. Before any dynamical behaviour of the antenna could be investigated, the static behaviour has to be understood at _rst. This is necessary to determi-nate the forces in the frame around the heart of the antenna, which is formed by a multiple Kap-ton membrane layer. A planar and at state without any wrinkling in the Kapton membrane is vital for the function. After the static simulation of the stress conditions in the boom and membrane the dynamic behaviour can be simulated. Main part of the modelling was to _nd a suitable way to build up a _nite element model of shell and beam elements for the frame. Naturally they both have some restrictions in usage which can be eliminated via intelligent modelling. Another chal-lenge was to _nd a simple model for constant force springs and plain woven fabrics. All this work is discussed and evaluated at the end of this research project, due to its use as prediction for a 1:3 scale testmodell. This model will be used to evaluate the results of this numerical investigation under a one-g environment and to evaluate the general design and function of this concept.